Pressure vessels and tanks useful for a variety of applications have long been made from synthetic resinous materials, such as epoxy resins, acrylic resins, and polyurethane resins, in combination with filaments having high tensile strength by impregnating such filaments with such resins. Such filament wound vessels are generally fabricated by winding a resin-impregnated fibrous strand around a rotating mandrel in a generally helical pattern in a number of superimposed layers. In some cases, the strand is wound over rounded or curved ends on the mandrel to form the heads of the vessel integral with the cylindrical wall or shell; in other cases, one or both heads are formed separately. Pressure vessels made in this manner can be constructed with adequate strength to withstand high internal pressure e.g. 150 to 1500 psig, and as such, they have found their usefulness in reverse osmosis, nanofiltration, microfiltration, and other types of crossflow fluid separation where a feedstream is supplied under pressure and undergoes membrane filtration to separate the feedstream into a permeate or filtrate stream and a concentrate stream. It has become relatively standard in the industry to provide tubular pressure vessels for such purposes that are essentially cylindrical in shape and that have end closures of a circular shape which can be locked in place after a plurality of cylindrical filtration cartridges have been inserted. U.S. Pat. No. 6,074,595 illustrates one such method for making such tubular pressure vessels, and U.S. Pat. No. 6,558,544 illustrates such a pressure vessel having circular end closures.
However, as the fluid separation industry has grown and progressed, and particularly where water separation to provide a potable water stream is involved, there have been continuing efforts to both reduce the number of plumbing connections in ordered arrays utilizing a multitude of such pressure vessels, as well as reduce the overall footprint of such an installation for space considerations. As one solution to this problem, a side port in one pressure vessel is desirably connected directly to a side port in an adjacent pressure vessel so as to, in essence, provide for a common feed to and/or a common discharge from a plurality of such aligned pressure vessels. Arrangement of interconnections between vessels in this manner can eliminate the need for manifolds which would supply an individual feed stream to each pressure vessel as well as manifolds which would collect and combine individual discharge streams from each pressure vessel. By such provision of side inlet and outlet ports in pressure vessels, it has been found that a plurality of such vessels can be very efficiently stacked and plumbed; thus, feeding to or collecting from a single vessel in the stack will allow the entire stack of vessels to be so serviced.
Now that this approach has become more generally accepted in this industry, there has become a desire to provide such side port connections in larger diameters so as to allow an even greater number of pressure vessels to be joined together in a horizontal or vertical stack of vessels without undue pressure drops at the interconnections. For a number of decades, a variety of approaches have been taken to providing side and end ports in filament wound pressure vessels of this general type. U.S. Pat. Nos. 3,106,940; 3,112,234; 3,293,860; 4,391,301; 4,614,279; 4,685,589; 4,700,868; 4,765,507; 5,900,107; 5,979,692; 6,074,595 and 6,179,154 show various methods which have been employed to provide ports in an end and/or sidewall of a pressure vessel that is being fabricated by a filament winding process. For example, annular fibrous patches bonded with a curable thermosetting resin have been applied to a partially formed vessel wall and carefully placed to surround the location where an opening is to be cut, as described in U.S. Pat. No. 3,106,940, whereupon one or more additional layers of sidewall are overwrapped. In many instances, an additional circumferentially wound annular patch is positioned in alignment with the first patch, followed by additional layers of the fibrous material then being wound or laid up over the second patch. In the final cured vessel, the patches have become embedded within the wall of the vessel, and the opening is then cut through the patched area. Although effective for lower pressure operation and smaller diameter ports, this method not only interrupts the fabrication process but also requires careful manual placement of the patches.
The '279 patent shows the application of a composite reinforcement patch or pad comprising alternating layers of woven material and random-oriented fibrous mat material which is applied directly to a thermoplastic vessel liner at a location desired for a side port, prior to the conventional filament overwinding operation, thereby placing this port-surrounding reinforcement between an interior thermoplastic liner and the exterior wound filament vessel. Once the winding operation is complete and the resin cured, an opening is cut through the filament wound tank wall in the region of the patch, and a fitting is installed by insertion through the opening and securing it in place by a washer and a threaded nut, or other fastener. Again this method is effective for small diameter ports and operation at low pressure, but it requires an interior liner and careful manual placement.
The '301 patent shows the reinforcement of the sidewall of a filament wound pressure vessel by first winding the vessel in its normal fashion and then carefully overwinding the filament wound vessel with a series of reinforcement bands 3 of filaments that will be cured along with the vessel sidewall. Pairs of these reinforcement bands 3 are wound around the vessel at approximately 25° angles at locations which flank an intended side port, and a pair of likewise flanking hoop reinforcement bands are overwound atop these pairs of angular reinforcing bands to complete the reinforcement. As depicted, the bands are carefully located so as to lie adjacent to and surround the hole that will be cut through the sidewall for a side port; thus, precise manual control and placement are required.
Although these various methods of installing side ports in a pressure vessel have been adequate for side ports of limited diameter, for example side ports up to about 5 cm in diameter, the installation of side ports greater than 6.5 cm has been troublesome from the standpoint of stability over the lifetime of the pressure vessel, particularly when the vessel was to be subjected to pressures about 150 psig and above. Often these prior art side port reinforcements would have a tendency to undergo laminar separation and/or movement resulting in failure and/or leakage at the side port. As a result, solutions were sought for this problem in order to facilitate the incorporation of relatively large side ports in tubular filament wound vessels, particularly in pressure vessels that will accommodate relatively high internal pressures, often as high as 800-1500 psig; in addition, solutions that would permit automated fabrication and not require interruption and/or careful manual control were a particular goal. By relatively large side ports is meant a side port having a diameter equal to at least about 35% of the interior diameter of the pressure vessel.